Make the releaseDateColumn field be true by default

[waldyrious]

Make the releaseDateColumn field be true by default

(Includes a commit removing the now redundant releaseDateColumn: true from all products/*.md files)

Fixes #6669

[waldyrious]

CI was failing until I explicitly added releaseDateColumn: false to ckeditor.md, readynas.md, robo.md and steamos.md in 2997a4f, as those seemed to be relying on the default value of the field being false.

However, I couldn't figure out what exactly are the triggering conditions, common to these files, leading to the failures. I'd like to add a note to CONTRIBUTING.md to explain in which cases releaseDateColumn needs to be set to false — something similar to:

endoflife.date/CONTRIBUTING.md

Line 333 in d73daca

# End Of Active Support date (mandatory if eoasColumn is true, else MUST NOT be set).

or

endoflife.date/CONTRIBUTING.md

Line 351 in d73daca

# End Of Extended/commercial Support date (optional if eoesColumn is true, else SHOULD NOT be set).

Any insights as to what might have been the cause(s) of the errors?